Turning is a process of industrial production obtained by machining. The turning is defined by a rotary motion of the workpiece and a motorcycle for mostly straight-line tool (milling and drilling tool has a rotating motion instead). The cutting edge penetrates the workpiece material and the excess off (allowance) forming a chip. The machine tool is used for turning the lathe.

The turning is used extensively in the processing of metals, but also for wood and stone. The issues described below relate mainly to the creation of pieces of metal, in particular, we relied on our experience in turning back of the bar with Cami range.

TYPE OF BORING:

According to the surface to be obtained, is turning into:

turning flat (or facing) surfaces perpendicular to the axis of rotation of the workpiece

turning conical tapered surfaces

turning cylindrical: cylindrical surfaces coaxial with the axis of rotation of the workpiece

turning spiral: helical surfaces, eg the execution of threads on the lathe

Turning to the form (or profiling): surface complex contours

According to the position of the tool is divided into:

external turning: machining of the outer part of the piece

turning Internal machining of the inside of a piece of cord

According to the degree of finish machining is called:

Rough: the first phases

Finishing: the final stages of processing

If the tool penetrates the workpiece you plunge turning, and if the tool removes the finished part from the rest of the material (bar unprocessed) is called truncation. Sometimes the piece comes off too soon while the remains of a material called witness turned.

In turning to copy, equipment with a probe is then drawn on a template, transmitting its motion to the tool so that it reproduces the profile on the workpiece. In turning with tool shape (or turning constant profile) is a tool used with a profile on the cutting edge that plays a negative piece on your profile.

The piece can also be set so eccentric for eccentric turning shares, for example, the cylindrical surfaces of a crankshaft.

TOOLS FOR LATHE:

Depending on their composition tool materials can be classified into:

carbon steels and low alloy steels, tool: that simple carbon steels and low alloy carbon steels with carbon content ranging from 0.90% to 1.30%, have high hardness (HRC 65-70), cold that once exceeded 200 ° decreases sharply.

high-speed steels and SuperFast: have a chemical composition comprising tungsten, chromium, vanadium and molybdenum in addition to the carbon contained in the percentage varying from 0.7% to 1.5%. Manganese and silicon content in percentages less than 0.5% while in the presence SuperFast you from 4% to 12% (max. 20%) of cobalt.

cast cobalt alloys: cast alloys (or star) are not steel, because they contain iron in limited quantities. The properties of cast alloys are very high hardness (HRC = 65-70) maintained at high temperature and low resilience.

sintered metal carbides and metal carbides coated: also known as hard metals are produced with the technology of powder metallurgy. They are characterized by high hardness (HRC = 78) maintained hot, from a great compressive strength. The main negative features are the low tensile strength, flexural and fatigue, in addition to low resilience. Allow to reach a high production rate, to work very hard materials, and these defects are easily remedied.

ceramic materials: also called cermets, which are obtained by powder metallurgy, and consist essentially of alumina (90-99%) and other metals or oxides or carbides. Although endowed with exceptional properties of hardness and cold and heat, are very fragile and should be used with appropriate cutting parameters

Cubic boron nitride (CBN): used to produce tools for the first time around 1970, the cubic boron nitride is a material of high hardness and wear resistance. Especially suitable for finishing hard materials such as hardened steels, tool steels, etc..

diamond allows the use of high cutting speeds (1000-6000 m / min), work for a very long time without wearing out and get mirror surfaces. Used mainly on materials such as aluminum, copper, bronze, etc..

The tools can be used whole (or consist of a single material, such as high speed steel tempered) or insert (made of several materials).

In the latter case, only the active part of the tool, the cutting head, consisting of a hard material, such as a hard metal (the so-called Carbide), alumina, boron nitride or diamond, and the passive part of the tool, the stem , is built tough and cheaper materials such as steel.

The cutting edge can be fixed to the shaft by welding, brazing through tough alloys with copper or silver (brazed tools) or by a mechanical fastening system with a screw, or lever bracket (holders). Today they are used mostly holders with inserts standardized forms, so you can replace a worn or broken inserts too reusing the same holders.

CHIP BREAKER FOR LATHES OR AVVOLGITRUCIOLO

During turning operations, especially in the machining of aluminum and mild steel, it forms a continuous chip that can cause damage to the cutting edge and danger to the operator. This does not apply to work performed by high-speed steel tools, because the low cutting speed allows you to monitor the progress of the chip. The drawback is eliminated by adopting one of two ways:

Avvolgitruciolo: the chip, an invitation made by the tool chest, is wrapped tightly around and then walks away.

Breaker: chip breaker tool is always made on the chest and consists of a step against which crashes into the chip breaking.

TOOL TIME DURING THE TURNING:

It defines the time duration of a tool a tool that can work at a certain cutting speed before being replaced or reground. Essential parameter for the duration of a tool is the cutting speed to vary from this range for wear and hence its duration. The report links the term of Taylor to the cutting speed:

where:

Vc = cutting speed in meters / minute

T = time in minutes between sharpness and the subsequent

n = constant depending on the material being processed and the material from which the tool is

Ct = constant depending on factors such as angles characteristic of the tool, refrigeration in use, depth of cut.

this report is to be considered with caution, as some authors recommend the application systems of use only in well-defined, and not in general. However, even if the cutting speed is the process parameter that affects more tool life, the Taylor equation can be modified to take into account other process parameters such as feed f (mm / rev) and the depth of cut d (mm), ottenedo this report:

where the exponents x and y (assume values ​​less than unity) are determined experimentally according to the cutting condition.

FITTING THE PIECES FOR TURNING

The workpiece can be mounted on the lathe in multiple ways to receive the rotary motion required for the work:

cantilever of chuck. In this case the thread shaft is mounted on the lathe chuck. It is suitable for processing a montage of short pieces, or for operations facing, cutting, drilling holes from the center or manufacturing axial.

between points, between the tip and tailstock. In this case the axis of the lathe is the tip mounted on the threaded shaft is screwed onto a disk equipped with an eccentric pin, said menabrida, moving the shank of the clamp (a terminal pear shaped), which in turn drags the workpiece. On the tailstock is inserted into the tailstock, which can also be rotating. To make this kind of installation on the two ends of the piece must first be performed from the center of the holes. Between the chuck and the tailstock. It is a combination of the two options.